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Unfortunately adding another boar to a bonded pair of boars is a recipe for disaster. Boars can only live in pairs and attempting to add a third will cause fights Between them. You will end up with the new piggy being alone. As a worst case scenario, it can also break the bond between your current two meaning you actually end up with three single piggies.
If you wanted more piggies, you would have to have a separate boar pair, in a separate cage. You couldn’t add any females either (two boys cannot live with any females as again it’ll cause fights) and any females in the same room (even though they would be in a separate cage) would also cause fights between your current two boys.